Excellent, it seems we've got a winner here. The only reason I even considered #1 was the OEM navigation. Credible sources suggest that it's difficult to retrofit one to a Seville.
I'm a huge fan of proper navigation systems, and by proper I mean ones that really provide useful route information and POIs. OEM systems have their pros and cons. The biggest advantage, naturally, is that they've been designed as a part of the car, and therefore fit perfectly and look great. The biggest disadvantage is that a navigation system is only as good as its software and maps. They should be kept up to date. Most of the time I end up using my cell phone as a navigator, as it has, among other things, an up-to-date speed camera database.
It's also more discreet, as it whispers the instructions straight into my headset. That leads people to believe that I have a great sense of direction. So the lack of OEM navigation isn't that big of a problem, if you're able to navigate without visual cues (I think she is), and don't need
a DVD player in your car (I think she can manage without one).
The wheels on car #1 would've been sold without a doubt, since I'm not a fan of ultra-low-profile tyres myself. Now I either need to locate a matching set of OEM wheels for the winter tyres, or buy two sets of good aftermarket ones for car #2. What I didn't realize at first was that those wheels might have caused actual damage to car #1. I want her first car to be reliable, as having a car sit in a shop for long periods of time really sucks the fun out of owning one. Believe me, I know.
As many of you pointed out, car #2 is much better value for money. Lower mileage for less money. I'm partial to black, but again, silver is a more practical color. Not that she wouldn't take good care of it though, I think she will.
I don't think head gaskets will be an issue here. Germans are very systematic, and these cars have been serviced at the dealer, and certified by the TÜV. I'll also take the one I'm buying to a place, where they'll assess the chassis, test the emissions etc. Again, I don't want to buy her a lemon.
Tomorrow is the big day then, I'll pay a "reservation free" for car #2. I'm really glad she has a unique taste, and likes the STS. We'd probably have a VW Golf or a Dodge Caliber in our driveway if she was more like her friends.
Thanks a million for your input guys, it really made a difference! Please let me know if you have more thoughts on this.